Marking wafers using pigmentation in a mounting tape

ABSTRACT

Wafer level techniques for marking the back surfaces of integrated circuit devices are described. A wafer mounting tape is provided that includes releasable pigments. The pigments can be released by exposing the mounting tape to a selected frequency of electromagnetic radiation (e.g., UV light). The released pigments mark the back surface of the wafer. The exposure and pigmentation may be controlled using a variety of techniques including servo control of a light source, the use of masks or reticles or other suitable techniques. The marking may be done on any suitable back surface material including polymeric backcoatings, metalized films or directly on semiconductor materials.

FIELD OF THE INVENTION

The present invention relates generally to the packaging of integratedcircuits. More particularly, the invention relates to wafer levelarrangements and methods for marking the back surfaces of semiconductordice.

BACKGROUND

There are a number of conventional processes for packaging integratedcircuits. One approach that is commonly referred to as “flip chip”packaging generally contemplates forming solder bumps (or other suitablecontacts) directly on the face of an integrated circuit die. In somesituations, the contacts are formed directly on I/O pads formed on thedie, whereas in other situations the contacts are redistributed. The dieis then typically attached to a substrate such as a printed circuitboard or package substrate such that the die contacts directly connectto corresponding contacts on the substrate.

In a number of packaging styles (including flip chip and other exposeddie wafer level packaging styles) it is desirable to mark the backsurface of the integrated circuit die/package. Depending upon thepackaging contemplated, these markings may be made directly on asemiconductor material or on a back coating (e.g., polymeric protectivecoating). Typical marking may include designations such as an indicationof the manufacturer or supplier of the devices, a part number, a “pin 1”designator, etc. To minimize costs, when possible, it is desirable tomark the devices at the wafer level.

In many applications the wafers are thinned (typically by backgrinding)in order to reduce the overall height of the resulting devices. As thedesired thickness of semiconductor devices is reduced, it can becomemore difficult to perform the handling operations necessary to process(e.g. mark) the wafer after thinning. In the semiconductor industry,there are continuing efforts to increase device yield per wafer or lotand reduce the costs and time associated with semiconductor fabricationand packaging. The present invention seeks to provide more efficientapproaches to marking the back surface of integrated circuits at thewafer level.

SUMMARY

To achieve the foregoing and other objects of the invention, wafer levelmethods of marking the back surfaces of integrated circuit devices aredescribed. In one aspect, a wafer mounting tape is provided thatincludes releasable pigments. The wafer mounting tape may be used tosupport a wafer during wafer sawing and/or other process operationduring the manufacture, packaging or testing of integrated circuits.

In some embodiments, the pigments used in the wafer mounting tape arearranged such that they can be released by exposing the mounting tape toa selected frequency of electromagnetic radiation (e.g., UV light). Thereleased pigments mark the back surface of the wafer. The exposure andpigmentation may be controlled using a variety of techniques includingservo control of a light source, the use of masks or reticles or othersuitable techniques. The marking may be done on any suitable backsurface material including polymeric backcoatings, metalized filmsand/or directly on semiconductor materials.

In some embodiments the mount tape can include a backcoat layer that isdesigned to permanently attach to the back surface of a wafer. In theseembodiments, the pigment layer may be sandwiched between the backcoatlayer and a mount layer so that any released pigments mark the backsurface of the finished wafer (and more particularly, the back surfaceof the backcoat layer).

As will be appreciated by those familiar with the art, there are avariety of releasable pigment materials that may be used as the tape'spigment layer. By way of example, a variety of pigment releasable epoxyresins work well. The epoxy resins may be applied to the mounting tapein either film form or paste form. Emulsion based pigmentationapproaches also work well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 illustrates in top plan view an exemplary wafer comprisingmultiple surface mount semiconductor dice.

FIGS. 2( a)–2(d) are diagrammatic cross sectional views of a wafer atvarious stages of production in accordance with an embodiment of thepresent invention.

FIG. 3 is a process flow diagram illustrating a method of packaging adie that facilitates applying a protective coating to the back surfaceof a wafer in accordance with one embodiment of the present invention.

FIG. 4 is a process flow diagram illustrating a method of packaging adie that facilitates applying a protective coating to the back surfaceof a wafer in accordance with another embodiment of the presentinvention.

FIG. 5 illustrates in top perspective view a surface mount semiconductordie scribed from the wafer of FIG. 1.

FIG. 6 is a process flow diagram illustrating a method of packaging adie that facilitates marking the back surface of a wafer in accordancewith another embodiment of the present invention.

FIG. 7 is a process flow diagram illustrating a method of packaging adie that facilitates marking the back surface of a wafer in accordancewith another embodiment of the present invention.

In the drawings, like reference numerals generally designate likestructural elements. Also, it should be understood that the depictionsin the figures are not to scale.

DETAILED DESCRIPTION

The present invention relates generally to a wafer level method ofapplying a protective coating to the back surface of a wafer. Generally,a layered tape is adhered to the back surface of the wafer. In theillustrated embodiments, the tape, which is referred to herein as abackcoat/mount tape, includes a first layer formed from a “backcoat”material that will be permanently affixed to the back side of the waferand a second “mounting” layer that effectively serves as a mounting tapesuitable for supporting the wafer during dicing operations. Thebackcoating layer is generally formed from a material that can be set orcured such that it may be permanently secured to the back surface of thewafer. The mounting layer is arranged such that it is strongly adheresto the backcoating layer until it is “released”, as for example, by UVirradiation. The described arrangement provides a good mechanism forapplying an opaque protective coating layer to the back surface of awafer.

Referring now to FIGS. 1–2 a representative method of applying aprotective coating to the back surface of wafer 100 will be described.FIGS. 2( a)–2(d), are diagrammatic cross sectional views of a segment ofa wafer at various stages in the process of applying a protectivecoating 206 to the back surface of a wafer 100 in accordance with anembodiment of the present invention. Initially, a wafer 100 isfabricated using conventional and/or appropriate wafer fabricationtechniques. A representative wafer 100 is diagrammatically illustratedin FIG. 1. The illustrated wafer 100 has a plurality of dice 102separated by horizontal and vertical scribe lines 104. Each of the dice102 includes a plurality of solder balls, contacts or “bumps” 106 thatare intended to be mounted directly onto contact pads of a substrate,such as a printed circuit board (PCB). The bumps 106 may be formeddirectly on I/O pads on the die or redistributed using conventionalredistribution techniques. It should be noted that while only arelatively small number of dice 102 are shown on the wafer 100 forpurposes of illustration, most wafers have significantly more diceformed thereon. By way of example, current state of the art waferstypically have several hundred to several thousand dice formed thereon,and some have more than ten thousand dice. As is well known in the art,most wafers and dice are formed of silicon, although any otherappropriate semiconductor material can also be used, including, forexample, gallium arsenide (GaAs), indium gallium phosphide, silicongermanium, and the like.

In many semiconductor applications it is considered desirable to reducethe height of the finished dice by “thinning” or backgrinding the waferafter fabrication. One conventional approach for thinning a wafercontemplates applying a backgrind tape 202 to the active (front) surfaceof the wafer 100 (step 306) and then grinding the back surface of thewafer (step 308) using conventional techniques to reduce the thicknessof the wafer. The resultant thinned wafer is diagrammaticallyillustrated in FIG. 2( a). In the illustrated embodiment, the backgrindtape 202 covers both the solder bumps 106 and the active surface 110 ofthe wafer 100. The purpose of the backgrind tape is to stabilize thewafer during a backgrinding process. In this example, the backgrindinghas all ready already been completed such that the wafer is at itsintended thickness. It should be appreciated that wafer thinning is anentirely optional step, although it is relatively common in modern flipchip and wafer level packaging manufacturing processes.

Once the wafer is at its desired thickness, a backcoat/mount tape 205 isapplied to the back surface of the wafer 100 as illustrated In FIG. 2(b). The backcoat/mount tape 205 includes of a backcoat layer 206 and amount layer 208. The backcoat layer 206 of the tape may serve severalpurposes. As an example, the backcoat layer 206 may be optically opaqueto protect the IC from light exposure. This is particularly useful inapplications where the die may be exposed after packaging. In someapplications, the backcoat layer 206 may also help reduce chipping ofthe substrate 204 during a singulation operation. As such, the backcoatlayer 206 may serve any of a number of functions. The mount layer 208 oftape 205 may also serve several functions including supporting the waferduring the testing/sorting of wafers (especially for very thin wafers),singulation as well as retaining the diced IC's for handling beforepicking.

In some embodiments, the backcoat layer 206 is formed from a curableadhesive such as an epoxy based adhesive material. As will be describedin more detail below, in various embodiments, the backcoat layer 206 maybe cured thermally, by UV irradiation or using other appropriatemechanisms. In other embodiments, the adhesive may be formed from athermosetting composition or any other material that adheres well to theback surface of the wafer and is generally compatible with both thewafer and the intended use of the resulting semiconductor devices. Whatis important is that the backcoat layer adheres firmly to the backsurface of the wafer so that it does not delaminate during subsequentfabrication steps or during use.

After the backcoat/mount tape has been applied, the backgrind tape 202may be removed and the wafer 100 may be diced using any of a number ofmethods known in the art. By way of example, wafer sawing, laser cuttingor other suitable singulation techniques may be used to dice the wafer.In the embodiment shown in FIG. 2( c), the singulation cut 210 is cut toa depth that fully divides the wafer substrate 204 and the backcoatlayer 206 of the tape 205, but only partially cuts or scores themounting portion 208 of the tape. In this manner, dicing proceeds untilall of the IC devices have been singulated. The mounting portion 208 ofthe backcoat/mounting tape 205 assures that the IC devices are securelyheld in place as a group, which may be desirable to facilitate testingand/or further processing at the wafer level.

Once all of the desired processing has been accomplished, the mountlayer of the backcoat/mount tape may be removed. As will be appreciatedby those familiar with the art, many conventional wafer mount tapes aredesigned to be sensitive to UV light such that they originally adherevery strongly to the wafer, but they become substantially less sticky tothe wafer after exposure to UV light. This property is particularlyuseful because the wafer mount tape adheres very strongly to the waferduring wafer processing (e.g. wafer sawing). Then, when wafer processinghas been completed, the mount tape may be exposed to UV light, whicheffectively releases the tape by making the adhesive substantially lesssticky. The exposed tape can then be readily removed from the backsurface of the wafer. As discussed further below, in the illustratedembodiments, mounting layer 208 of the backcoat/mount tape 205 alsopreferably exhibits a releasing property such that when the mountinglayer is “released”, it may readily be separated from the backcoat layerwhich in turn is securely affixed to the dice 102. Although UVreleasable tapes are most common in semiconductor applications, itshould be appreciated that other suitable releasing mechanisms, such asthermally or chemically releasable tapes may be used as well.

After the mounting layer 208 of backcoat/mount tape has been released,the dice 102 may be picked from the mount tape (or the mount tape may beotherwise removed) thereby leaving a number of singulated dice. FIGS. 2(d) and 5 are diagrammatic cross sectional and perspective views ofrepresentative singulated dice 102 after the mount tape has beenremoved.

The described backcoat/mount tape can be used to efficiently, quicklyand inexpensively apply a protective coating to the back surface of awafer. The thickness of the resulting protective coating 306 depends inlarge part on the thickness of the backcoat layer 206 and thereforegenerally can be controlled by defining the thickness of the backcoatlayer 206 in the backcoat/mount tape. The thickness of the backcoatlayer and the resulting protective coating 306 may be widely variedbased on the perceived needs of any particular situation. By way ofexample, protective coating thicknesses in the range of 5 to 50 micronsare readily obtainable. Notably, protective coating films having athickness of less than approximately 25 or 30 microns are readilyobtainable. As will be appreciated by those familiar with applyingprotective coatings to the back surface of a wafer, these thicknessesare generally less than (potentially significantly less than) thethickness of screen or stencil printed protective coatings, which tendto be more in the range of 40 to 125 microns. In many currentapplications, coatings having thicknesses in ranges on the order 15 to30 microns are desirable.

Since the described tape applied protective coatings can generally bethinner than screen and/or stencil printed coatings, they can be curedor set faster than printed coatings. This can be a significant advantageduring production because it can take several hours (e.g. 8–10 hours) toapply and cure a printed protective back coating. Such a delaysignificantly slows the wafer production process. In contrast, thedescribed tape applied protective layers can be applied and cured morequickly, which is a significant advantage.

Referring next to FIG. 3, a representative wafer finishing process thatincorporates the present invention will be described. In this particularembodiment, the protective coating (backcoat layer) is thermally curedand the mounting layer is UV cured. Initially, a wafer is fabricated ina conventional manner in step 302. As noted above, a wafer willtypically have several hundred to several thousand dice formed thereon,and some have more than twenty thousand dice. The wafer may then bebumped in operation 304. Bumping is a process by which solder balls of aselected size are formed in electrical connection with the wafercontacts. Bumping may be accomplished by any number of methods known inthe art. After the wafer is bumped at operation 304, backgrind tape 202may be applied to the active surface 110 of the wafer 100 at operation306. The backgrind tape allows the wafer to be held firmly in placeduring a backgrind operation. Backgrinding allows the wafer to bebrought into conformance with a desired thickness. It should beappreciated that as the size of electronic devices shrinks, so too mustthe attendant components of those devices. Backgrinding may beaccomplished by any of a number of methods known in the art.

After backgrinding, a backcoat/mounting tape 205 is applied to the backsurface of the wafer 100 at operation 310. Generally, the backcoat layer206 is directly adhered to the back surface of the wafer that has beenbackground as in operation 308. However, it can also be appreciated thatbackgrinding is not an absolutely necessary operation as the wafer maybe in conformance to a desired thickness without backgrinding. Once thebackcoat/mounting tape 205 is secured to the wafer, the backgrind tape202 may be removed at operation 312. The removal of the backgrind tape202 from the active surface of the wafer 110 exposes the solder balls106 and therefore allows for probing of the wafer 100 as well as anyother subsequent manufacturing processes and/or operations.

After the backgrind tape 202 is removed, the backcoat layer 206 may becured at step 314. Curing the backcoat layer 206 completes its adhesionto the back surface of the wafer 100. That is, curing the backcoat layer206 securely and permanently bonds the backcoat layer 206 with the wafer100. Curing may be accomplished in multiple ways depending on the natureand type of backcoat material used as well as on the composition andcharacteristics of the wafer. In the illustrated example, the backcoatlayer is thermally cured.

It should be appreciated that if the backgrind tape 202 is removedbefore curing as described above, then the uncured backcoat layer 206 ofthe backcoat/mounting tape 205 should adhere more strongly to the waferthan the backgrind tape 202 since otherwise, removal of the backgrindtape 202 will tend to separate the wafer from the backcoat/mounting tape205. In alternative embodiments, the backgrind tape 202 can be removedafter backcoat layer has been cured. In still other embodiments, thebackgrind tape 202 can be removed before the backcoat/mounting tape 205is applied.

In the described embodiment, the mount layer 208 is formed from asubstantially clear or transparent UV curable adhesive material such asa suitable epoxy based or polymeric composition. With a clear mountlayer 208, the back surface of the wafer 100 may be laser marked atoperation 320 with the mount tape still in place by shining the laserthrough the mount layer. In this manner, laser marking may be done atthe wafer level. It should be appreciated that the marking is done onthe cured backcoat layer 206 through the clear mount layer 208. Lasermarking is generally well known in the art and allows for a high degreeof accuracy. However, as will be appreciated by those familiar in theart, laser marking is not traditionally done through a mount tape. Aswill be described in more detail below, marking through the mount tapehas several advantages. Even in embodiments where the mount tape is notsubstantially transparent to the laser, the back surface of the wafermay still be marked with the backcoat/mount tape in place by burningthrough (or charring or partially burning through) the mount layer.

After the wafer 100 is marked at operation 320, the wafer 100 may thenbe diced or singulated at operation 322. Dicing is the process ofseparating IC devices residing on a wafer. The size of individualdevices is variable and depends on the configuration requirements of themanufacturer. Dicing may be accomplished in any of a number of suitablemanners including sawing or laser cutting. As can be seen in referenceto FIG. 2( c), the singulation cut 210 fully separates both the deviceand the backcoat layer 206. However, the cut preferably does not fullycut through the mounting layer 208. In this manner, the individualdevices, which are typically quite small, are held in place by themounting layer. The devices may then readily be tested or furtherprocessed at the wafer level as desired for a particular device.

After the wafer 100 is diced at operation 322 and any other desiredwafer level processing or testing is completed, the mounting layer 208may then be released by exposure to UV light at operation 324. As willbe appreciated by those familiar with UV releasable epoxies, exposingthe mounting layer 208 to UV light significantly reduces the adhesiveproperties of that layer so that the individual devices 102 may beremoved from the mounting layer 208 while allowing the backcoat layer206 to stay on the backside of the singulated ICs. Once the mountinglayer has been released, the individual devices 102 may be picked andplaced as desired.

A representative individual semiconductor die 102 scribed from the waferis shown in top perspective view in FIG. 5. Each die 102 preferably hasa plurality of solder bumps 106 formed on an active face 110. It shouldbe appreciated that although only one “row” or “ring” of solder contactsor bumps is provided on the die in the illustrated embodiment, othercontact patterns including, for example, multiple rows, multiple rings,or arrays of contacts may also be provided as desired.

The backcoat/mounting tape 205 may be formed in any suitable manner. Byway of example, the backcoat layer may be applied in either paste orfilm form to a conventional mount tape.

Referring next to FIG. 4, an alternative method of applying the backcoatlayer will be described. This embodiment is somewhat similar to theembodiment described above with respect to FIG. 3. However, the backcoatlayer 206 is formed of a UV curable material (such as a UV curableepoxy) and the mount layer 208 is formed from a clear UV releasablematerial (such as a UV releasable epoxy). With this arrangement, boththe curing of the backcoat layer and the releasing of the mount layermay be accomplished in the same operation. As in the previouslydescribed embodiment, the backcoat layer may be applied to the mountingtape in either film form or paste form.

In this embodiment, the wafer may be fabricated and then bumped and/orbackground as desired in a manner similar to previously described.Thereafter, the backcoat/mounting tape 205 is applied to the backsurface of the wafer in step 410. In this embodiment, the backgrind tapewill be removed and the wafer will be diced prior to the curing of thebackcoating layer. Therefore it is important that the backcoat layeradhere quite well to the wafer even prior to curing so that the removalof the backgrind tape does not pull the backcoat/mount tape 205 from thewafer and the wafer is held solidly in place during the dicingoperation.

Once the backcoat/mounting tape 205 has been applied, the backgrind tape202 may then be removed in operation 412 and the wafer may be lasermarked in operation 420. Again, it should be appreciated that the orderof these steps may be readily reversed. For example, it may be desirableto remove the backgrind tape 202 prior to the application of thebackcoat/mount tape.

Once the wafer has been marked and the backgrind tape removed, the wafermay be diced in operation 422. Like in the previously describedembodiment, the dicing cuts entirely through the wafer and the backcoatlayer of tape 205, but only scores or partially cuts through themounting layer of tape 205. After the wafer has been diced, it may beexposed to UV light in operation 424 to both finally cure the backcoatlayer and release the mounting layer. The dice may then be picked andplaced as desired.

In some embodiments, a single UV exposure can be used to both cure thebackcoat layer and release the mounting layer as illustrated withrespect to FIG. 4. However, it is often preferable to utilize atwo-stage UV exposure wherein the dosage of the first exposure isarranged to cure the backcoat layer and the second exposure is arrangedto release the backcoat layer. This can be accomplished by usingmaterials that are activated by different frequencies of UV light or bycontrolling the dosage levels. In embodiments where a two-stage UVexposure is used, the process flow may be more similar to the flowdescribed above with respect to FIG. 4 except that the first stage ofthe UV exposure (curing the backcoat layer) is done at step 314 beforethe wafer is diced. This is advantageous in many situations to insurethat the backcoat layer adheres strongly to the wafer during thesingulation process, particularly if wafer sawing is used to dice thewafer.

In the previously described embodiments, a two layered backcoat/mountingtape 205 has been used. In other embodiments additional layers may beprovided in the backcoat/mounting tape. By way of example, the use of aspecific three layer tape will be described with respect to FIG. 6. Asin the previously described tapes, the upper layer is a backcoat layerand the lower layer is a transparent mount layer. The middle layer is apigment layer that may be selectively activated to mark the back surfaceof the wafer (and more particularly, the back surface of the backcoatlayer). As will be appreciated by those familiar with the art, there area variety of releasable pigment materials that may be used as the tape'spigment layer. In the described embodiment, the pigment layer is formedfrom a releasable pigment material that may be released by exposure toUV light. By way of example, a variety of known pigment releasable epoxyresins may be used. The epoxy resins may be applied to the mounting tapein either film form or paste form. By way of example, suitablereleasable pigment epoxy resins are available from Dexter Hysol,Loctite, Ablestik and/or Advantge Epoxy Composites. Alternatively,emulsion based pigmentation approaches may be used as well.

From a process standpoint, a manufacturing process using a backcoat tapewith a pigment layer may be very similar to the processes describedabove with respect to FIG. 4 or 5. In the embodiment illustrated in FIG.6, a packaging process flow similar to the flow described above withrespect to FIG. 3 is illustrated. However, instead of laser marking thebackcoat layer (e.g., step 320 of FIG. 3), when it is time to mark thewafer, the desired pigmentation is activated. The activation of thepigment may be accomplished using servo control of a laser or throughthe use of a mask or reticle that is positioned over the wafer. Themask/reticle is patterned with a positive image of the desired marking.As will be appreciated by those skilled in the art, it is common to markthe wafer with part numbers, trademarks, pin markings (e.g. pin 1markings) and/or other appropriate designation information. With themask or reticle in place, the back surface of the wafer (or a selectedsegment thereof) is exposed to UV light at a frequency that causes theexposed portions of the pigment layer to release. (Step 620). It shouldbe appreciated that the mount layer of the tape is substantiallytransparent (at least to the wavelengths of light used to release thepigment layer). Therefore, the UV light passing through the mask canreadily pass through the mount layer of the tape in order to release thepigments. The release of the pigment marks the adjacent portions of thebackcoat layer, which causes the back surface of the wafer to be markedin a manner that matches the mask. In this way, the wafer can be markedin any way desirable. A variety of pigments may be used. By way ofexample, green and white pigments work well. In alternative embodiments,the marking may be done without the use of a mask or reticle using servocontrol of a laser or other appropriately constrained light source.

After the wafer has been marked, the wafer may be sorted, tested, diced,and/or otherwise processed in accordance with the needs of a particularapplication. When appropriate, the mount layer may be released aspreviously described. Preferably, the pigment releasing mechanism isdesigned to activate at a different frequency than the mount tapereleasing mechanism. This prevents the pigment from being releasedduring the mount tape exposure, which could cause pigment to cover theentire back surface of the wafer. Conversely, although it is preferable,it is generally not as important to insure that the mount tape does notrelease during the pigment releasing exposure. This is because mostmarking operations are designed to mark a relatively small percentage ofthe back surface of each die (and thus a relatively small percentage ofthe back surface of the wafer). Therefore, given the strength of thebond of the mount tape, even if the marked portion of the wafer isreleased, the mount tape will still be able to hold the wafer (dice)firmly in place during wafer sawing.

In the illustrated embodiment, the pigmentation is applied to apolymeric backcoat layer that is part of the mounting tape. However, itshould be appreciated that the advantages of the use of pigmentation arenot limited to use with mounting tapes that include a backcoat layer.Rather, a pigmentation layer may be used as part of any mounting tape.In these embodiments, the marking may be applied to any back surface ofa wafer. Thus, by way of example, the pigmentation may be applied to thebare back surface of a wafer (i.e., directly on a semiconductormaterial), to a polymeric backcoating applied using other techniques, toa metalized back surface of a wafer, or any other coating thatconstitutes the back surface of a wafer.

Referring next to FIG. 7, yet another embodiment of the invention willbe described. In some of the previous described embodiments, it waspointed out that the back surface of the wafer (e.g., the backcoatlayer) can be laser marked through the mount tape. The principle oflaser marking through a mount tape can be extended beyond embodimentswhere a backcoat layer is applied through the use of a backcoat/mounttape as well. For example, plain back surfaces, metalized back surfacesor backcoatings applied using other techniques can all also be markedthrough a clear mount tape. By way of example, FIG. 7 illustrates amethod of laser marking the back surface of a wafer. In this embodiment,the wafer is laser marked through a clear mount tape that does notinclude a backcoat layer. In this embodiment, the packaging process flowmay continue in a manner similar to the process described above withrespect to FIG. 4. However, in this embodiment, the back surface of thewafer is metalized (after any desired backgrinding) as illustrated instep 709. By way of example, the back surface may be metalized bysputtering a metal film such as titanium on the back surface of thewafer. The metallization is performed prior to the application of themount tape (710).

Marking a wafer through the mount tape is particular advantageous inthin wafers. As will be appreciated by those familiar with the art, somecurrent designs call for thinning the wafers to thicknesses on the orderof as little as 2 mils for unbumped wafers or 5 mils for bumped wafersand it is expected that thinning wafers to thicknesses of less thanapproximately 1 mil will become more common in the near future. Thehandling of such thin and delicate wafers becomes a significant problem.Therefore, it can be very helpful if various post thinning operation canbe accomplished while the wafer is supported by a mount tape. Markingthe back surface of a wafer through the mount tape allows the wafer tobe better supported during the handling required to mark the wafer.

Although marking the wafer through a clear mount layer (in multiplelayer mount tapes) or a clear mount tape (in single layer tapes) isgenerally preferred, it should be appreciated that in other embodiments,the laser may actually burn the mounting layer/tape (or portionsthereof) during the marking process. That is, even if the mountinglayer/tape is not substantially transparent to the laser, marking maystill be done at the wafer level by burning through (or charring orpartially burning through) the mount tape without defeating thefunctionality of the mount tape. This is largely because typically onlysmall portions of each die are marked and thus even if the region of themounting tape that is marked loses its adhesiveness, the mount tapestill can securely hold the wafer in place.

It should be appreciated that non-pigment based laser marks aregenerally made by burning or charring or otherwise causing atransformation of the surface to be marked. In embodiments thatincorporate a backcoat layer in the mount tape, the mark is made byburning or charring the backcoat layer in a manner that leaves anoticeable mark. In other embodiments a different surface is burnt orcharred to leave noticeable mark.

Although only a few embodiments of the invention have been described indetail, it should be appreciated that the invention may be implementedin many other forms without departing from the spirit or scope of theinvention. These representative embodiments described above are providedto aid in the understanding of the invention. It should be apparent tothose skilled in the art that the present invention may be practicedwithout some or all of these specific details. In other instances, wellknown process operations have not been described in detail in order toavoid unnecessarily obscuring the present invention.

For example, in the primary described embodiments, the backcoat layer206 is formed from a curable material. However, this is not arequirement. Rather, the backcoat layer could be formed from athermosetting resin or any other suitable adhesive material that adhereswell to the back surface of a wafer. In some embodiments, it may bedesirable to use a B-stageable adhesive as the backcoat layer so thatthe adhesive can be partially cured prior to the dicing operation andfinally cured during the mounting layer releasing operation (e.g. UVexposure). Although the primary described embodiments contemplate theuse of a UV releasable mounting layer, it should be appreciated thatthermal or chemical releasing mechanisms could be used as well.

In another aspect of the invention, various methods of marking the backsurface of a wafer with a mount tape in place have been described. Theseinclude incorporating a pigment releasable material into the mount tapeand laser marking through the mount tape. Although these embodimentshave been described primarily in the context of marking wafers having aprotective coating on their back surface, the marking can also bereadily used to mark the back surface of a bare wafer. The marking maybe done on metalized back surfaces, polymeric coatings or any othercoating applied at the wafer stage.

In the discussions of the embodiments illustrated in FIGS. 3, 4, 6 and7, specific ordering of the steps have been described. However, itshould be apparent that in many situations, several of the steps (e.g.,bumping, backgrinding, laser marking, etc.) are entirely optional andthat several other steps (e.g., sorting, testing, applying underfill orsolder ball support layers to the active surface of the wafer, etc.) maybe added without departing from the invention. Additionally, it shouldbe apparent that the order of many of the steps may be varied.Therefore, the present embodiments are to be considered as illustrativeand not restrictive and the invention is not to be limited to thedetails given herein, but may be modified within the scope andequivalents of the appended claims.

1. A wafer level method of marking back surfaces of integrated circuit devices, the method comprising: providing a wafer having a plurality of flip chip style integrated circuit devices, the wafer having an active surface and a back surface, the active surface having a plurality of electrically conductive pads; applying a mount tape to the back surface of the wafer, the mount tape being arranged to support the wafer and including a optically opaque backcoat layer, a pigment layer and a mount layer; curing the backcoat layer such that the backcoat layer is affixed to the back surface of the wafer and such that the backcoat layer covers the entire back surface of each of the integrated circuit devices; exposing selected portions of the mount tape to light at a frequency that releases pigments from the pigment layer to thereby mark the backcoat layer to thereby mark the back surface of the integrated circuit devices; dicing the wafer to define a multiplicity of singulated flip chip style integrated circuits dice supported by the mount tape; and separating the singulated integrated circuits dice from the mount tape while leaving the backcoat layer affixed to the back surfaces of the integrated circuit dice, whereby the cured backcoat layer forms an optically opaque protective coating that covers the entire back surface of each integrated circuit device and is suitable for preventing light from striking the back surface of the integrated circuit device and the pigments that mark the backcoat layer include markings desired for the integrated circuit device.
 2. A method as recited in claim 1 wherein the backcoat layer is formed from a polymeric material.
 3. A method as recited in claim 1 wherein the mount tape utilizes a UV releasable adhesive that is optimized to most efficiently release under exposure to a frequency of light that is different than the frequency used to release pigments from the pigment layer.
 4. A method as recited in claim 1 further comprising positioning a mask or reticle over the mount tape and wherein the light used to release the pigments is exposed through the mask or reticle to selectively mark selected portions of the back surface of the wafer.
 5. wafer level method of marking back surfaces of integrated circuit devices, the method comprising: providing a wafer having a plurality of integrated circuit devices, the wafer having an active surface and a back surface, the active surface having a plurality of electrically conductive pads; applying a mount tape to the back surface of the wafer, the mount tape being arranged to support the wafer and including a pigment layer and a UV releasable adhesive, the pigment layer being arranged such that exposure to light at a designated frequency causes release of pigments from the pigment layer, and the UV releasable adhesive being optimized to most efficiently release under exposure to a frequency of light that is different than the frequency used to releases pigments from the pigment layer; exposing selected portions of the mount tape to light at a first frequency that releases pigments from the pigment layer to thereby mark the back surface of the wafer; dicing the wafer to define a multiplicity of singulated flip chip style integrated circuits dice supported by the mount tape; and after both the pigment releasing and dicing steps are completed, exposing the mount tape to light at a second frequency different than the first frequency in order to release the UV releasable adhesive.
 6. A method as recited in claim 5 further comprising sputtering a metal film on the back sure of the wafer to form a protective metal film on the back surface of the wafer and wherein the pigment marks the protective metal film.
 7. A method as recited in claim 5 wherein the pigment directly marks a semiconductor material. 